The invention is based on a fuel injection pump of the general type described hereinafter. Such fuel injection pumps, also known as in-line injection pumps, such as Type PES . . . MW . . . made by Robert Bosch GmbH, have a laterally closed pump housing, which in its side walls has only the required inflow and outflow bores but no openings for use during assembly. The pump elements are inserted from above into the associated receiving bores, while the tappets and tappet springs with their associated spring plate, as well as the regulating sleeves, are inserted into their corresponding receiving bores from below through the opening in the bottom of the pump housing. To enable the installation and removal of the regulating sleeves, each receiving bore has an assembly recess, opening into the longitudinal recess for the governor rod. In these fuel injection pumps, Type PES . . . MW . . . , these assembly openings are each embodied by one assembly groove machined into the wall of each receiving bore, but the assembly groove extends somewhat eccentrically in the surface on which the tappet that drives the pump piston runs. These assembly grooves are cut into the pump housing specifically for the purpose of removing the regulating sleeve. Similar assembly grooves are also known from British Pat. No. 642,736, in which they are intended to enable the removal of the pump pistons which are provided directly with guide arms. Assembly grooves which simultaneously act as guide grooves for sliding blocks serving to secure the tappets against twisting are known from Austrian Pat. No. 218 790 and also from the in-line injection pump, Type PE . . . P . . . , of Robert Bosch GmbH, Stuttgart (see Bosch Technical Manual on Diesel Injection Pumps, Types PE and PF, VDT-U 2/1 De of June, 1981).
In all these fuel injection pumps, the surfaces on which the tappets run are interrupted by assembly or guide grooves, and as a disadvantageous consequence of this interruption of the running surface, the maximum possible load can be imposed on these injection pumps only in one operating direction, for instance clockwise. For counterclockwise operation, lesser loads are prescribed, because as a result of the obliquely exerted cam drive force the tappet is always pressed against the same side of the wall.